The present invention relates to embedding digital data in encoded digital data and, in particular, to a method and apparatus therefor.
More and more information is becoming available in digital form, whether the information be video or audio entertainment, video or film images, computer programs or computer generated information, literary material or other data content or programming, and the sources thereof include the Internet, CD-ROMs, DVDs, terrestrial and satellite broadcasting, and the like. Such digital information is of greater interest to hackers and thieves who seek to obtain or appropriate such content or program by other than legitimate means owing to the ability of data or information in digital form to be copied many times without loss or corruption of the data or information. Such high-quality copies can be made by pirates and others quickly and at virtually no cost other than that of the recording medium.
One defense against such acts is provided by security schemes, such as firewalls, anti-copying schemes, encryption and the like, which are intended to provide an obstacle or barrier to prevent the unauthorized copying of the protected digital information. Complementary to security schemes are identification schemes that provide unique identifying characteristics to the digital information so that if it is copied or pirated, the copy will contain the identifying characteristic which may be used to prove the source and origin of the copied file, e.g., to authenticate the identity of the copyright owner. A physical analog to this is to engrave the owner""s name on a physical object. Preferably the identifying information is hidden so that a pirate or thief will not recognize it and so will not obliterate it in an attempt to preclude tracing the copied content to its rightful owner. A physical analog to this is the marking of automobile parts with the serial number of the automobile, usually in unobvious or hard to find places, for subsequently identifying stolen cars and parts thereof.
Information may be encoded for transmission in digital form by any number of encoding schemes, such as the encoding standards promulgated by the International Standards Organization, Geneva, Switzerland, for example, International Standard ISO/IEC 13818-1, xe2x80x9cInformation Technologyxe2x80x94Generic Coding or Moving Pictures and Associated Audio: Systems,xe2x80x9d commonly referred to as MPEG-2 Systems, and International Standards ISO/IEC 11172-2 and ISO/IEC 13818-2, xe2x80x9cInformation Technologyxe2x80x94Generic Coding or Moving Pictures and Associated Audio: Video,xe2x80x9d commonly referred to as MPEG-1 Video and MPEG-2 Video., respectively.
Identification information is conventionally embedded in information coded in the MPEG-2 standard, for example, by slightly modifying pixel samples for groups of audio or video pixels during signal coding in a way that is hopefully not apparent in the reproduced data when properly decoded. This technique is often referred to as xe2x80x9cdigital water markingxe2x80x9d due to its similarity to the conventional water marking of papers to provide a visual indication of the manufacturer or originator thereof (e.g., as for stationery), or the authenticity of a document or instrument made thereof (e.g., stock certificates and currency). Whether the embedded digital watermark information is inserted into the video signal itself (pixel-domain techniques) or in the compressed MPEG or MPEG-like video bitstream (compressed domain techniques), the video quality is necessarily degraded to some extent in that noise-like patterns are superimposed on the video, usually at levels below the visual threshold of a typical viewer.
Although conventional water marking may be inserted either during or after compression of the data by MPEG-2 coding, certain disadvantages arise because it is in the pixel domain. For example, MPEG compression may degrade or remove the watermark (although the watermark should be able to survive moderate additional decoding and recoding). In addition, the watermark must be at a low level so as to not to be apparent in or degrade the decoded data, such as the reproduced image or other data, and so is limited to a very low bit rate, e.g., only 64 bits/frame or less, and is not useful where a higher bit-rate is desired, e.g., 150-340 bits/frame or higher. Moreover, water marking is easily detected and mapped, and then removed, if one has access to two copies of the same data, such as an unwatermarked original and a watermarked copy or two differently watermarked copies.
Accordingly, there is a need for identifying or other information to be inserted into coded digital data in a way that does not degrade the decoded data. It is also desirable that the bit rate of the inserted information be substantially higher than that available with conventional data water marking.
To this end, the method of the present invention is for embedding data in a coded bitstream wherein the coded bitstream has at least one syntax element that can be coded in plural positions, the value thereof coded in one position being overriding respecting the value coded in the other position, which method comprises:
coding a value of the one syntax element in the overriding syntax element position; and
inserting the embedded data into the other syntax element position.
According to a further aspect of the invention, a coder for embedding data in a coded bitstream having headers and data blocks wherein the coded bitstream has at least one syntax element that can be coded in a header and in a data block position, comprises means for coding a bitstream having at least one syntax element that can be coded in a header and in a data block position, wherein the value thereof coded in one of the header and the data block positions is overriding respecting the value coded in the other of the header and data block positions, means for coding a value of the one syntax element in the overriding one of the header and data block positions, and means for inserting the embedded data into the other of the header and data block positions.